Aluminum die casting alloy



United States Patent Office 3,150,967 ALUMTNUM DEE CASTHNG ALLGY Joseph A. Woltering, Cincinnati, and Dudley Fished, Hamilton, hio, assignors to Hamilton Die Cast, Inc, Hamilton, @hio, a corporation of Ghlo No Drawing. Filed July 24, 1961, Ser. No. 125,949 8 Claims. (Cl. 75-441) This invention relates to an aluminum die casting alloy.

As far as we know, there has heretofore been known no aluminum die casting alloy which could be successfully anodized both decoratively and protectively. Past alloys have been particulraly deficient in their ability to be decoratively color anodized. The reason for this appears to have been due to the presence of a substantial amount of silicon in such alloys. Silicon has heretofore been considered necessary in aluminum die casting alloys to impart suitable flow characteristics to the alloy, and because it prevents hot-shortness in the alloy, which is the tendency of a die casting alloy to crack or split upon solidification. Silicon forms an eutectic in the alloy and imparts stretchability to it with the result that the alloy does not craze or crack as it solidifies from the molten state. In the absence of a fairly large proportion of silicon, for example -10 weight percent, previously known aluminum die casting alloys have tended to be hot short. However, the presence of silicon in an aluminum die casting alloy in an amount sufilcient to prevent hot shortness renders the alloy unable to be successfully anodized, and especially poor in its ability to be color 9 anodized and hard anodized. Silicon-bearing aluminum die casting alloys darken on clear anodizing, and present a nonuniform dark gray surface. The process of anodizing is basically a process of chemically changing the surface layer of an aluminum object from aluminum to its oxide. Silicon will not oxidize under this process and, therefore, with a silicon content of 5 to 10% in an aluminum alloy casting, 510% of the surface area, being silicon, rejects the anodic coating. This has been a serious defect in past alloys, since color anodized aluminum presents a hard, smooth, bright finish which is very desirable on many products.

We have discovered a non-silicon bearing alloy which, without loss of tensile, yield, and elongation properties within the normal range for aluminum die casting alloys, displays no tendency to hot shortness and, moreover, which will take an excellent clear or color anodized finish.

The alloy We have discovered is believed to be a rather radical departure from past die casting alloys. On a weight basis, it comprises 5.0 to 5.9% zinc, 1.8 to 2.2% copper, 1.8 to 2.0% iron, .04 to 2% manganese, the remainder being aluminum of at least commercial purity. Trace or small percentages of magnesium,-lead, nickel, titanium, tin and chromium may be present. Silicon may be present in an amount not exceeding about 0.5%.

Specific analyses of several melts of alloys in accordance with this invention are as follows:

3,150,967 Patented Sept. 29, 1964 We have found that the combination of zinc, copper, and iron in the ranges indicated will form an eutectic in place of the silicon which has in the past been utilized, and moreover does not render the alloy unable to be anodized.

The iron content of this alloy is considerably higher than that of other aluminum die casting alloys. We have discovered that an iron content of the quantity indicated prevents the alloy from soldering or sticking to the casting die. Nonetheless, iron fallout is low, and it is believed that the low manganese content is responsible for this characteristic. A small amount of titanium e.g. 0.03%, refines the grain structure of the alloy.

Typical die castings made of this alloy display an ultimate tensile strength of about 37,000 p.s.i., a tensile yield strength of about 24,000 p.s.i., and an elongation in 2" of about 5 /2%.

This alloy displays good die casting characteristics, although it should be cast in a vacuum for best results.

In addition to its other properties, castings made of an alloy in accordance with the present invention can be porcelain enameled, inert are welded, dip brazed, chromium plated, and hard anodized. No other aluminum die casting alloy is believed to possess all of these properties.

What is claimed is:

1. A die castable, anodizable alloy consisting essentially of about 5.0 to 5.9% zinc, 1.8 to 2.2% copper, 1.8 to 2.0% iron, 0.04 to 0.2% manganese, and the balance aluminum of at least commercial purity.

2, An alloy in accordance with claim 1 includes about 0.03% of titanium.

3. An alloy in accordance with claim 1 includes about 0.10% of nickel.

4. A1 alloy in accordance with claim 1 includes about 0.03% of tin.

5. An alloy in accordance with claim 1 includes about 0.18% of chromium.

6. A die castable, anodizable alloy consisting essentially of about 5.5 to 5.8% zinc, 1.8 to 2.2% copper, 1.8 to 2.0% iron, 0.04 to 0.1% manganese, not more than about 0.5% silicon, 0.06% magnesium, and 0.09% lead, and the balance aluminum.

7. A die castable, anodizable alloy consisting essentially of about 5.5 to 5.8% Zinc, 1.9 to 2.2% copper, 1.8 to 2.0% iron, 0.04 to 0.1% manganese, not more than about 0.5% silicon, 0.06% magnesium, and 0.09% lead, 0.11% nickel, 0.04% titanium, 0.04% tin, and 0.18% chromium, and the balance aluminum.

8. A die castable, anodizable alloy consisting essentially of about 5.5% zinc, 2.2% copper, 1.9% iron, 0.3% silicon, 0.05% manganese, and the balance commercially pure aluminum.

which also which also which also which also References Cited in the tile of this patent UNITED STATES PATENTS 1,352,271 Jeih'ies et al. Sept. 7, 1920 2,075,090 Bonsack Mar. 30, 1937 2,290,017 Bonsack July 14, 1942 OTHER REFERENCES New Jersey Zinc Company, Die Casting for Engineers, New York, 1942, page 27. 

1. A DIE CASTABLE, ANODIZABLE ALLOY CONSISTING ESSENTIALLY OF ABOUT 5.0 TO 5.9% ZINC, 1.8 TO 2.2% COPPER, 1.8 TO 2.0% IRON, 0.04 TO 0.2% MANGANESE, AND THE BALANCE ALUMINUM OF AT LEAST COMMERCIAL PURITY. 